Precast thin concrete slab type structures are commonly used in constructing roof, floors, and concrete decks. They generally take the shape of concrete slabs which may have a t-shape in cross section. There is a horizontal portion of the slab which is the load bearing surface and there is generally reinforcing mesh or bars within the slab. There is at least one generally flat surface or edge that adjoins a flat surface or edge of a confronting adjacent slab. The top surface of the slab is usually kept rough to be ready to receive a cast in place composite concrete topping with topping reinforcements which is a minimum 2 inches thick.
When the concrete slabs are placed next to each other to form the deck, it is possible for the slabs to move with respect to each other. This is due to construction loading, wind forces or thermal expansion. In order to prevent or minimize the relative movement and to increase the strength of the final structure, metal inserts, often called “weldments” are placed within the concrete slabs with a portion of the weldment extending out from an edge of the slab. When the slabs are positioned for final assembly, the metal weldment of one slab is aligned with and opposite to a complementary metal weldment in an adjacent slab (see FIGS. 7 and 8). The complementary metal weldments are welded to each other to join the two weldments. This results in a unitary structure that is much stronger and less prone to movement than if no means of joining the slabs were used. While designing the connection and the weldment, the following aspects are considered:                (A) horizontal shear capacity (Vh) to provide the diaphragm force,        (B) tensile capacity (T),        (C) vertical shear force (Vv) to resist the uneven loading between adjacent slabs,        (D) concrete coverage of slab reinforcement to be maintained before the topping is installed in the field,        (E) ease of placement of the loose welding steel and ease of welding, and        (F) overall material cost.        
Various types of weldments have been used in the past. Once such type which has been used is illustrated in U.S. Publication No. 2003/0140590 to Lancelott, III et al. This is a U-shaped thin steel plate that had two arms of the “U” embedded within the concrete and the base of the “U” exposed along the edge of the concrete slab. Due to its pointing shape, the arms often are pulled out from the slab when under tensile load. This is unacceptable as it substantially weakens the overall structure.
Another weldment which has been used is illustrated in U.S. Pat. No. 5,402,616. This type of weldment solved some problems except its vertical arms are deep which sacrifices the concrete coverage above the slab reinforcement especially when the total slab thickness is thin. This type of weldment is very helpful for thick slabs that have sufficient space to provide concrete coverage above the slab reinforcement, but it provides unacceptable coverage for thinner slab structure.
Another weldment is illustrated in U.S. Pat. No. 6,854,232. The vertical arms of this type of weldment are rotated almost 90 degree to make room for the weldment, slab reinforcement and its concrete coverage. A major problem with this weldment is that at the extreme degree bend location, a hinge point is created which reduces the vertical shear capacity of the weldment and creates localized spall beneath or above the weldment. This reduces the strength of the weldment.
Thus, there is the need for a concrete weldment having improved securing properties over the weldments illustrated in the prior art that results in the weldment being more securely retained within the thin concrete slab with proper slab reinforcement's concrete coverage, even when the weldment is subjected to vertical and horizontal forces. Applicant's invention provides an increased weldable area, at the proper angle to the concrete surface for easier welding proposes, and allows for thermal expansion of the weldment without cracking and spalling the concrete.
Applicant's invention solves the problems stated above by providing a weldment that comprises a central plate which defines the weldable surface. The central plate is at approximately 30 degree angle with respect to the vertical edge of the concrete slab which solves the problems of providing an easily accessible weldable surface. There are shear force reinforcing members at both ends of the central plate. The reinforcing members are designed to minimize the twisting length in order to avoid interfering with the slab reinforcement mesh or reinforcing bars that are placed in the slab. The maximum amount of twisting or rotation is limited to 45 degree in order to preserve the vertical and horizontal shear capacity as well as to keep the slab reinforcement means well protected with proper concrete coverage. There is a pair of outstanding arms extending out from each of the ends of the shear reinforcing members. Each of the outstanding arms has a 90 degree bend at the ends of the arms which provide for increased pull out tensile capacity of the weldment.